Phytoestrogens: A Review of Their Impacts on Reproductive Physiology and Other Effects upon Grazing Livestock

Abstract

Legume crops and pastures have a high economic value in Australia. However, legume species commonly used for grazing enterprises have been identified to produce high concentrations of phytoestrogens. These compounds are heterocyclic phenolic, and are similar in structure to the mammalian estrogen, 17β-estradiol. The biological activity of the various phytoestrogen types; isoflavones, lignans and coumestans, are species-specific, although at concentrations of 25 mg/kg of dry matter each of the phytoestrogen types affect reproductive functions in grazing livestock. The impacts upon fertility in grazing livestock such as cattle and sheep, vary greatly over length of exposure time, age and health of animal and the stress stimuli the plant is exposed to. More recently, research into the other effects that phytoestrogens may have upon metabolism, immune capacity and growth and performance of grazing livestock has been conducted. Potential new benefits for using these phytoestrogens, such as daidzein and genistein, have been identified by observing the stimulation of production in lymphocytes and other antibody cells. Numerous isoflavones have also been recognized to promote protein synthesis, increase the lean meat ratio, and increase weight gain in cattle and sheep. In Australia, the high economic value of legumes as pasture crops in sheep and cattle production enterprises requires proactive management strategies to mitigate risk associated with potential loss of fertility associated with inclusion of pasture legumes as forages for grazing livestock.